The present invention relates in general to centrifugal pumps for pumping blood in an extracorporeal blood circuit, and, more specifically, to a pump with a magnetically levitated impeller and with disposable and reusable portions that is applicable to blood pumps for short-term heart assist, especially following heart surgery.
During cardiac bypass surgery, if a patient's heart is slowed or stopped for surgical repair, his or her blood must be artificially oxygenated and pumped through the body using an extracorporeal support circuit. Using this system, venous blood is diverted from entering the right chambers of the heart and is instead directed through a series of tubes, pumps, and filters, which provide fresh oxygen to the blood and return it to the body's systemic circulation at the aorta. The oxygenated blood is then circulated throughout the body. The circuit thus ensures that the patient continues to be nourished by oxygenated blood flow while the heart is unable to function.
In performing such a procedure, a complicated apparatus is required. One or two blood reservoirs, an oxygenator (possibly combined with a heat exchanger), a blood pump, and multiple tubes to connect the various components are needed and must be assembled and arranged before surgery may begin. Typically a significant amount of time must be spent just prior to surgery to accomplish the set-up, and great attention must be paid to the details of this complicated task. In order to ease this task, a nearly complete support circuit is often assembled by the manufacturer in a sterile condition and packaged in a manner that protects sterility until the time that it is needed for a procedure. An assembly pack having a frame for supporting the individual disposable processing elements (e.g., filters, pump, oxygenator) and the interconnecting tubing is shown in U.S. Pat. No. 6,811,749, which is incorporated herein by reference in its entirety. Such a frame pack provides for quick set-up and integration into a complete extracorporeal support system, thus enhancing operating room efficiency.
Most of the components of the extracorporeal blood circuit are disposed of following the surgical procedure as medical waste since they have been exposed to the blood of the patient. Even relatively more expensive components such as a centrifugal pump are disposed of because the difficulty and cost of re-sterilization would be too great.
Centrifugal blood pumps are increasingly used in artificial heart/lung units for extracorporeal blood circulation. Centrifugal pumps of the magnetic coupling type wherein a driving torque from an external motor is transmitted to an impeller through magnetic coupling are commonly used because the physical communication between the blood chamber of the pump and the exterior can be completely excluded and invasion of bacteria is prevented. The centrifugal blood pump includes a chamber having a blood inlet port and a blood outlet port and an impeller rotatably accommodated in the housing to increase the difference between inlet and outlet fluid pressure by means of centripetal acceleration generated during its rotation. The impeller has one or more permanent magnets disposed thereon which are acted upon by attracting magnets of a drive motor that is disposed adjacent to the impeller chamber. Typically, the impeller rotates without contacting the housing by magnetically levitating above the bottom of the chamber. A separate set of levitating magnets that may include electromagnets is disposed axially and/or radially relative to the impeller in order to provide a precisely controlled levitating field. Position sensors are used to provide position feedback to a controller which drives the electromagnets. Tight tolerances and close distances between the impeller and the levitating magnets and sensors must be maintained in order to achieve proper pump functioning. Examples of magnetically levitated centrifugal blood pumps include U.S. Pat. Nos. 6,575,717; 6,589,030; 7,212,550; and 7,128,538, and U.S. patent application publication 2005/0014991 A1, all of which are incorporated herein by reference in their entirety.
It is often preferable to locate the levitating magnets and position sensors above (i.e., at the top of) the impeller chamber, opposite from the driving motor, especially when device volume is to be minimized, as in an implant application. However, with the impeller chamber sandwiched between other structures, it has not generally been segregated as a separate disposable element. Making a disposable impeller chamber (i.e., pump head) which is insertable into a nondisposable pump drive unit is especially difficult with drive components above and below the pump head, because of the desire to have all the tubing for the circuit pre-connected to the pump as part of a frame pack. Therefore, centrifugal pumps of this type have typically been used for long-term applications and have been disposed of with the rest of the hardware components.